Liquid crystal display device

ABSTRACT

A plurality of character forming segments are affixed to one surface of a front and back plate of a liquid crystal device. Three conductors affixed to one of the plates are each coupled to approximately one-third of the segment electrodes affixed to that plate. A plurality of conductors are affixed to the other plate and are each coupled to three of the segment electrodes affixed to that plate. Liquid crystal material is disposed between the two plates. By making use of the display device and a disclosed keyboard scanning circuit, an eight character position liquid crystal display device and a keyboard may be coupled to an electronic calculator chip disposed in a standard twenty-eight pin package.

This is a continuation of application Ser. No. 799,808, filed May 23,1977 now abandoned.

BACKGROUND OF THE INVENTION

A type of visual display device coming into prominent use incorporatesso-called liquid crystals. Liquid crystals are a class of organicliquids which exhibit some properties of ordered crystalline structurewithin certain temperature ranges. One class of liquid crystals nowreceiving considerable attention is nematic liquid crystals which whenused in a dynamic scattering mode are transparent to visible light butwill become cloudy or opaque as a result of electrical current flowtherein. The current flow is believed to rearrange the orientation ofthe liquid crystal molecules resulting in scattering of incident light.Field effect operation of liquid crystals is also known, such as theso-called "twisted nematic" mode. Some of the materials suitable for usein Liquid Crystal Displays (LCD's) are disclosed in U.S. Pat. No.3,716,289 by L. T. Creagh et al, and U.S. Pat. No. 3,655,270 by L. T.Creagh, both assigned to the assignee of the present application.

Visual displays of letters or numbers can be formed using a thin (0.5 to1.0 mil) layer of a dynamic scattering mode nematic liquid crystalsealed between two sheets of glass. For the reflective type of displaypanel conductive transparent electrodes on the inside surface of thefront sheet and a transparent or highly reflective electrode on theinner surface of the back sheet are provided for each digit. When atransparent electrode is used on the back sheet, a highly reflectivemedium, such as aluminum foil, for instance, is preferably disposed onthe rear of the sealed display unit. When a voltage is applied to theopposing electrodes causing a current to flow in the liquid between theelectrodes, the liquid loses its transparency in that region thuspresenting to an observer an image in the shape of the electrodes fromtransmitted or reflected light. For the transmissive type of displaypanel the structure is similar, however, the back electrodes must betransparent and a light source is placed behind the panel.

In twisted nematic field effect LCD's, a similar structure is used, butlight polarizing media, analyzer and polarizer, are used with the frontand back sheets of glass, respectively. Linearly polarized lightpropagating perpendicular to the display is rotated 90° as it passesthrough the liquid crystal when no external electric field is beingapplied. By crossing the analyzer and the polarizer, light will passinto the display, reflect off the reflective medium and pass back out ofthe display when no field is present. By energizing appropriatesegments, dark characters on a light background appear. By arranging theanalyzer and polarizer in a parallel configuration, light is permittedto pass through the display only in presence of an electric field, thenby energizing appropriate segments, light characters on a darkbackground appear.

The voltage applied may be either D.C. or A.C., but A.C. voltages arepreferably used with liquid crystal displays because it has been foundthat D.C. voltages tend to shorten the useful life of LCD's compared toA.C. voltages.

Further, the pairs of opposing electrodes may be arranged such that allof the segments of the display are energizable at the same instant, assuggested by the electrode arrangement disclosed in FIG. 1 of U.S. Pat.No. 3,771,855, which patent is assigned to the assignee of thisinvention. Still further, displays using multiplexed scanners fordriving LCD's are known in the prior art, for example, U.S. Pat. No.3,999,180 teaches a multiplexed LCD system. But these systems when usedwith eight character displays have not been compatible with chipsdisposed in standard twenty-eight pin packages. For example, incalculator applications, two of the twenty-eight pins are set aside forthe power supply (i.e. battery) connections to the chip, leavingtwenty-six pins for driving the display. However, when the eightcharacter, eight segment (seven segments for the digit and one segmentfor the decimal point) per character position LCD is utilized, the priorart multiplexing methods for driving the display have required more thantwenty-six pins.

It was, therefore, one object of this invention to improve themultiplexing methods used with LCD's. It was another object to dispose acalculator chip capable of driving an eight character, eight segment percharacter, LCD in a standard twenty-eight pin package.

The foregoing objects are achieved as is now described. For an LCDresponsive to a one-third duty cycle drive, a total of sixty sixsegments are provided with twenty two segment select lines and threedrive lines. The sixty six segments are arranged into eight charactersof seven segments per character (56 total segments), and either eightsegments for decimal points for each character position, a minus signsegment and an annotator segment (e.g. memory indicator or errorindicator) or seven segments for decimal points for all but the leastsignificant digit position, a minus sign segment and two annotatorsegments. The total number of pins for such light character positionLCD's is 25.

Other embodiments of liquid crystal displays are taught as well as amethod for actuating the display and strobing a keyboard corrected tothe segment drive lines.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objects and advantages thereof, will bebest understood by reference to the following detailed description ofillustrative embodiments thereof when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 depicts in representative form a segment forming a conductorpattern used on a prior art liquid crystal display;

FIG. 2 is a sectional view through a liquid crystal display adapted forusing twisted nematic liquid crystal material;

FIG. 3a depicts one embodiment of a segment forming conductor patternfor use with a chip having reduced pin-out requirements;

FIG. 3b defines the various segments of a character;

FIG. 4 depicts another embodiment of a segment forming conductorpattern;

FIG. 5 is a diagram of a chip with reduced pin-out requirementsinterconnected with a LCD and a keyboard;

FIG. 6 shows the segment, drive line and scanning potentials for a fivevoltage level LCD display system;

FIGS. 7a-7d show the potentials of FIG. 6 in greater detail;

FIGS. 8a-8d depict another embodiment of the segment, drive line andscanning potentials for a five voltage level LCD display system;

FIG. 9 depicts the segment drive line and scanning potentials for a fourvoltage level LCD display system;

FIGS. 10a-10b show the potentials of FIG. 9 in greater detail; and

FIGS. 11a-11b depict another embodiment of the segment, drive line andscanning potentials for a four voltage level LCD display system.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown, in representative form apattern of conductors 2a and 2b deposited on the top and bottom glassplates (not shown) of a liquid crystal display device 2 of the typeheretofore known. The portions of the conductors forming charactersegment electrodes are shown with diagonal lines, while those portionswhich are to interconnect the character segments are shown without suchdiagonal lines. It should be remembered, of course, that the conductorsare preferably transparent and the segment portions of the electrodesarwe shown here with diagonal lines merely for the sake of clarity. Itis to be appreciated that the conductor patterns 2a and 2b are depositedon transparent substrates, 3 and 4 (FIG. 2) such as glass, whichsubstrates are sandwiched together and the region between substratesfilled with a nematic liquid crystal. Of course, the conductor patterns2a and 2b deposited on the substrates are in contact with the nematicliquid crystal, which is sealed between the substrates by a boundary ofepoxy cement or other sealing means. It should be evident to thoseskilled in the art, that LCD 2 is formed by the conductor patterns 2aand 2b is a one-third duty cycle display, that is, any segment of acharacter thereof is actuated by electrical signals only one-third ofthe time. However, given the time response of liquid crystals, aone-third duty cycle display appears to be constantly actuated to thehuman eye.

AC signals are preferably sequentially supplied to drive lines 5a, 5b,and 5c while AC signals are also selectively applied to segment lines6a-6y. Thus, to form the character "3" in the least significant digitposition, for instance segment lines 6a and 6c would be actuated whendrive line 5a is actuated, segment lines 6a and 6c would then beactuated when drive line 5b is actuated and finally segment line 6cwould be actuated when drive line 5c is actuated; this sequence is thenrepeated, the period thereof being approximately 7.5 msec. As can beseen, this sequence of select line actuation actuates segments A and Bfor one-third of the time, C and G for another third of the time and Dfor another third of the time, the segments being identified accordingto FIG. 3b. As can be further seen from FIG. 1, a display utilizing thisprior art conductor layout requires three separate drive lines 5a-c andtwenty-five separate segment lines 6a-6y. Considering that a calculatorchip driving display 2 would also require at least two power supplyconnections, it can immediately be seen that such a chip cannot bemounted in a twenty-eight pin package and also drive the display 2.Further, since in the prior art, separate keyboard lines were used tointerface the calculator chip with a keyboard 14 (FIG. 5), chips forcalculators having liquid crystal displays are being disposed inpackages having forty or more pins.

The one-third duty cycle display of FIG. 1 is commonly used with liquidcrystals operated in the twisted nematic mode. The present invention isdirected to display system operated on low duty cycles, such as thetwisted nematic LCD, but it should soon be evident to those skilled inthe art that the present invention is not limited to twisted nematicLCD's, but may be utilized with displays generally having low duty cyclecharacteristics.

Referring now briefly to FIG. 2, there is shown a sectional view of atwisted nematic type liquid crystal display 2. The liquid crystaldisplay 2 comprises a front plate or substrate 3 and a back plate orsubstrate 4 separated by a spacing layer and sealing means 19 forming anenclosed cavity for liquid crystal material 16 between the front andback plates. Conductor segments A, G and D, as identified in FIG. 3b,are shown in FIG. 2. A light source 17 provides light for the display 2.A viewer of the display 2 is generally identified by numeral 18. A firstlight polarizing media 20, commonly referred to as an analyzer isdisposed between viewer 18 and liquid crystal 16. A second lightpolarizing media 21, commonly referred to as a polarizer, is disposedbetween liquid crystal 16 and a reflective medium 22, which is generallyattached to the rear of the display.

Although various types of liquid crystals may be utilized in forming theliquid crystal display 2, nematic liquid crystals have generally beenused. Inasmuch as specific examples of nematic liquid crystals are knownto persons skilled in the art, such liquid crystals are not described indetail herein.

The front and back plates 3 and 4 of the liquid crystal display 2 aregenerally disposed in parallel and separated by a spacer 19 which servesto seal the liquid crystal material between the front and back plates.The separation of the plates depends upon the particular liquid crystalmaterial utilized and the voltage levels used to strobe the segmentelements; however, separations on the order of five to seventy-fivemicrons are known and voltages as low as three to four volts are known.The conductors are preferably transparent; tin oxide may be used for theconductor material.

When operated with crossed analyzer 20 and polarizer 21 and when nodrive and segment voltages are applied to the conductors, light fromlight source 17 generally passes through display 2 and thus a viewer isunable to see any characters. However, when the drive and segmentvoltages applied to the conductors are of sufficient magnitude andduration, the molecules of liquid crystal material 16 between thesegments on the front and rear plates 3 and 4 will align in thehomeotropic state. Thus, the liquid crystal material 16 disposed betweenappropriately energized conductor segments on the front and rear platesceases to rotate the light passing therethrough and the crossedanalyzer/polarizer extinguishes the light, causing the energizedsegments to appear dark to viewer 18.

When operated with parallel arranged analyzer/polarizer, the light anddark areas of the display are reversed. That is, appropriately energizedsegments appear as light areas on a dark background.

For further discussion of the operation of twisted nematic and othertypes of liquid crystal devices, referenc should be made to "LiquidCrystal Displays" by L. S. Goodman in the Journal of Vacuum Science andTechnology, Vol. 10, No. 5, September/October 1973.

Referring now to FIG. 3a, there is shown a one-third duty cycle liquidcrystal display 7 having conductor patterns 7a and 7b, which, as will beseen, requires only twenty-five interconnections with a calculator chip.Subsequently, a method for inputting data at a matrix keyboard 14 (FIG.5) using the display segment lines will be explained. The chip 15driving display 7 may, as will be seen (FIG. 5), be easily disposed in astandard integrated circuit package having twenty-eight pins. Conductorpattern 7a is coupled to three drive lines 8a-8c. Drive line 8a iscoupled to the A, B, and F segments of all character positions, exceptfor the most significant character position where it is coupled to the Bsegment. Again, the segment positions are identified in FIG. 3b. Driveline 8b is coupled to the C, E, and G segments in all characterpositions except for the most significant character position where it iscoupled to the C segment thereof. Drive line 8c is coupled to thedecimal point segments; the D segments in all character positions; theA, E, F, and G segments of the most significant character; the minussign segment and the memory indicator segment. Segment lines 9a, 9d, 9g,9j, 9m, 9p, 9s, and 9v are coupled to respective B, C, and decimal pointsegments in each character position, except for select line 9v which iscoupled to segment G of the most significant character in lieu of adecimal point segment. Segment lines 9c, 9f, 9i, 9l, 9o, 9r, and 9u arecoupled to respective A, D and G segments for all character positionssave the most significant character position. The segment lines 9b, 9e,9h, 9k, 9n, 9q, and 9t are coupled to respective E and F segments foreach character position, except the most significant character position;segment line 9t is also coupled to the decimal point segment for themost significant character. Segment lines 9b', 9e', 9h', 9n' and 9q' arerespectively coupled to the A, D, E and F segments of the mostsignificant character, the memory indicator segment and minus signsegment. As can be seen from FIG. 5, segment lines 9b', 9e', 9h', 9k',9n', and 9q' are respectively connected with segment lines 9b, 9e, 9h,9k, 9n, and 9q. This interconnection may be affected within display 7 orexternal to display 7 as is shown in FIG. 5, as a matter of a designchoice.

Thus, display 7 requires only three drive lines 8a-8c and twenty-twosegment lines 9a-9v to provide an eight character position display withdecimal points, minus sign and memory indicators. Inasmuch as eachcharacter and decimal point therefor comprise eight segments, plus twosegments for the minus sign and memory indicator, a total of sixty-sixsegments fully populates this three by twenty-two multiplexing scheme.As can be seen from FIG. 3a, the error indicator has been eliminated inthis embodiment; however, error indication may be provided by calculatorchip 15 by flashing display 7, for example, during an error condition.Alternatively, it should be evident to those skilled in the art that thememory indicator or decimal point segment for the least significantdigit position could be exchanged for an error indicator segment.

Referring now to FIG. 4, there is shown another embodiment of aone-third duty LCD. This LCD 12 has eight character positions with noerror, minus sign, memory indicator or decimal point indicator for theleast significant digit position. Drive lines 10a-10c are connected tothe character segments in much the same manner as drive lines 8a-8c inFIG. 3a except that all the segments of the most significant characterposition are connected to drive line 10c. Similarly, segment lines11a-11t are connected in the same manner as segment lines 9a-9t in FIG.3a, except that segment lines 11a', 11b', 11e', 11h', 11k', 11n', and11g' are connected to the G, B, A, C, D, E and F segments of the mostsignificant character. The segment lines with primes are again connectedto their unprimed counterparts. As can be seen, display 12 is aone-third duty cycle liquid crystal display having three drive lines10a-10c and twenty-one segment lines 11a-11t for providing a fullypopulated sixty-three segment display using a three by twenty-onemultiplexing technique. For this type of eight character display,negative numbers are limited to seven digit positions with the segment Gof the most significant character position being used for a minus signindicator.

Referring now to FIG. 5, there is shown a simplified schematic drawingof a calculator chip 15 for driving the liquid crystal display 7 of FIG.2, calculator chip 15 being interconnected with a matrix type keyboard14. As can be seen, chip 15 is provided in a standard twenty-eight pinintegrated circuit package, twenty-five pins interconnecting with liquidcrystal display 7 and matrix keyboard 14, two pins being provided forpower connections and another pin being unused in this embodiment. Ascan be seen, matrix keyboard 14 is interconnected with selected segmentlines 9a-9v for scanning or strobing the column conductors 14a and rowconductors 14b of matrix keyboard 14. Of course, the particular segmentlines used as well as the number of keyboard positions provided inmatrix keyboard 14 utilized is also a design choice; however, a matrixkeyboard which is both inexpensive to manufacture and which may be usedin the practice of this invention is disclosed in U.S. Pat. No.4,005,293, which issued Jan. 25, 1977 and which is assigned to theassignee of this invention.

Referring now to the upper portion of FIG. 6, there is shown voltagepotentials on drive lines 8a-8c. Also, the voltage on a normal segmentline when (1) three segments are off, (2) three segments are on and (3)two segments are on and one segment is off are also depicted. Thesesegment line voltages are referred to as "normal" to differentiate themfrom the scanning segment lines used to scan matrix keyboard 14, whichare explained below. As can be seen, the normal segment line (all threesegments off) is in phase with the positive and negative going pulses onthe three drive lines 8a-8c. It should be evident to those skilled inthe art, that the D.C. component on any segment is zero and that theR.M.S. value of the A.C. component on any segment is not sufficient toactuate that segment. The next normal segment line (all three segmentson) is, of course, out of phase with the pulses on the drive lines,thereby increasing the R.M.S value of the A.C. voltage supplied to eachsegment to a level sufficient to actuate those segments. Again, the D.C.component is zero. The third normal segment line (two segments on, onesegment off) is shown as being in phase with drive line 8c and out ofphase with drive lines 8a and 8b whereby the R.M.S. value of the A.C.voltage applied to the segments associated with drive lines 8a and 8b isof sufficient level to actuate those segments while the R.M.S. value ofthe A.C. voltage supplied to the segment associated with the drive line8c is insufficient to actuate that segment. Now, for example, if thedrive lines voltage as shown in FIG. 6 were applied to display 7 (FIG.3a) and the "all segments off" segment line voltage were applied tosegment line 9b, the "all segments on" voltage were applied to segmentline 9c and the "two segments on, one segment off" voltage applied tosegment line 9a, the number "3" (with no decimal point) would appear inthe least significant digit position of display 7. Based on theforegoing discussion, it will be evident how the segment lines 9a-9v ofdisplay 7 are selectively energized with A.C. signals to actuate thevarious segments in display 7 to communicate desired information to theviewer thereof.

It will be evident to those skilled in the art that the aforementionedsystem for actuating an LCD is the so-called five voltage level system;that is, the drive lines and segment lines produce the followingpotentials, where V is equal to 1.0 to 1.4 volts or more depending uponthe LCD requirements: 0 v, 1 v, 2 v, 3 v, and 4 v.

Having explained how display 7 may be normally actuated, it will now beexplained how the segment lines may be used for the purpose of strobingor scanning keyboard 14 without hindering display operation. It has beenfound that because of the response characteristics of liquid crystaldisplays, short duration, periodic, high frequency bursts of data may besuperimposed on either the display drive or segment lines withouteffecting the information displayed. In order to minimize any effect ondisplayed information, the following restraints are preferably imposedupon such a burst data system:

(1) the data bursts should preferably add no D.C. component to thesignals appearing across the segments;

(2) the R.M.S. component of the burst signal should be preferably smallin comparison to the R.M.S. component of signals actuating that display;and

(3) the display should be preferably blanked when the actuation of a keyis detected.

These constraints are preferably imposed for the following reasons, itbeing understood that the keyboard scanning system to be explained isoperable even if such constraints are not observed:

(1) DC components tend to shorten display life,

(2) as the R.M.S. components of the burst signal increase compared tothe R.M.S. components of an actuation signal, the contrast ratio of thedisplayed data is adversely affected; and

(3) if the display is not blanked, the coupling of two segment linesduring the actuation of a key at the keyboard will tend to cause theobservance of undesired character patterns at the display.

Referring again to FIG. 6, at the lower portion thereof, representationsof the voltages on scanning segment lines are shown for the same threecases as is depicted for normal segment lines, that is, (1) all segmentsoff, (2) all segments on, and (3) two segments on, one segment off. Inthis embodiment of the invention, the burst of data is applied intimed-relation to the pulses on drive line 8a. Here the burst of data isa pulse having a period of approximately 20 microseconds and occurringin timed relation to the leading edge of pulses on drive line 8a. In theembodiment depicted in FIG. 6, these pulses are shown occurring atapproximately the same instance as the occurrence of a leading edge ondrive line 8a. As can be seen, these pulses are preferably added in apositive going direction for a positive going voltage on drive line 8aand in a negative going direction for a negative going voltage on driveline 8a, whereby no D.C. component is added to the voltages sensed bythe segments of the display. Further, these pulses are of short durationcompared to the drive line pulse whereby the R.M.S. contribution by thepulse is small compared to that of the drive line voltages and segmentline voltages for an actuated segment. The burst pulses are shown asoccurring in timed-relation to the pulses on a drive line; however, itshould be evident to those skilled in the art that the burst pulse couldalso be generated in timed-relation to the pulses occurring on thesegment line (as opposed to the drive line), but it is believed thatusing the drive line for controlling the occurrence of the pulses onscanning segment lines simplifies the control circuitry needed therefor.

It has been mentioned that the scanning pulses preferably occur in afixed time relationship with respect to the pulses on drive line 8a.Referring now to FIGS. 7a-7c, FIG. 7 shows a drive line and scanningsegment line (all segments off) as previously shown in FIG. 6. FIGS. 7band 7c depict the signals on the scanning segment line (all segmentsoff) in greater detail. As can be seen from FIGS. 7b and 7c, the pulsemay occur approximately at the leading edge of the drive line pulse (atreference A) or a predetermined time thereafter (at references B, C or Dfor instance). In practicing the invention, one scanning segment line isprovided with the reference A pulse, another with the reference B pulse,another with the reference C pulse and so forth. These differentscanning segment lines are then applied to separate column conductors14a of matrix keyboard 14 (FIG. 5). When a keyboard switch is depressed,the pulse is communicated to a row conductor 14b and depending uponwhich row conductor the pulse occurs upon and further depending on thetiming of the pulse with respect to the leading edge of the pulses ondrive line 8a, the particular key depressed is decoded by sensingcircuit means on chip 15. To assure that the scanning pulses are notmasked from the sensing circuit means by the segment line signalsnormally occuring on segment lines, the potential on the sensing segmentlines is permitted to float during the period that the scanning pulsesare being generated on scanning segment lines as depicted in FIG. 7d;that is, the normal segment line voltage is temporarily disconnectedduring the time that the sensing means must be able to sense thescanning pulses. Also during this time, the sensing segment lines shouldpreferably be coupled to a small load to prevent inadvertent response ofthe sensing circuit means to circuit noise.

As was previously mentioned, the calculator preferably blanks thedisplay immediately after a key depression is detected so that undesiredsegments are not actuated in the display during keyboard operations.

In the embodiment of FIGS. 6 and 7 positive going pulse A occurs intimed-relation with the leading edge of the pulse on drive line 8a andis of approximately twenty microseconds duration. It is followed byapproximately 60 microseconds of voltage at the 1 v potential beforereturning to the 3 v potential. The height of the scanning pulse isshown as going to the 4 v potential. However, the potential selected isa matter of design choice.

The negative going pulse at A' may or may not be sensed by the circuitmeans as a matter of design choice; however, it is preferably insertedinto the scanning segment line signal along with the pulse at A toeliminate or reduce the D.C. component, for the reasons aforementioned.In FIG. 7c, there is shown a scanning segment line (all segments off)with the scanning pulse occurring at the reference B and B' positions.In FIG. 7d, the eighty microsecond float occurring opposite thereference A, B, C and D and the reference A', B', C' and D' pulses tominimize D.C. voltages at the display segments is shown.

Referring now to FIGS. 8a-8d, there is shown another embodiment of afive voltage level system with scanning pulses. This embodiment differsfrom the embodiment of FIGS. 6, 7a-7d in that the scanning pulses A-Dand A'-D' instead of being of a complementary relationship to minimizeD.C. voltages across display segments, are shown here as always beingadded with the same polarity. Given the display drive line potentials ofthe embodiment of FIGS. 6, 7a-7d, this would then result in some D.C.being coupled to the display segments. In this embodiment, the displaydrive line potentials are permitted to float during each approximately80 microsecond period that scanning pulses are generated to eliminateany D.C. component which would otherwise be contributed.

The drive line potentials with float during the approximately 80microsecond periods are shown in FIG. 8b. Segment line potentials forall segments off, with scanning pulses at times A and B, respectively,are shown in FIGS. 8c and 8d.

It will be appreciated that these keyboard scanning techniques areapplicable to other liquid crystal display driving techniques as well asthe five voltage level system just described. For instance, in FIG. 9,there is shown the potentials on three drive lines and three exemplarysegment lines for a four voltage level LCD system. The four voltagelevel LCD system voltages may be derived from the five level system ofFIG. 6, by using the same voltage levels of FIG. 6 for the period that apositive pulse is on any one of the drive lines and by adding a voltageequal to 1 V to all voltage levels during the time that a negative goingpulse is one of the drive lines. These two periods are identified by theReference A's and Reference B's in FIG. 9 for ease of understanding. Thedata burst, or data pulse of this invention may be applied to the fourvoltage level system of FIG. 9 in the same general manner asaforementioned. In FIGS. 10a and 10b, as it would occur on a scanningsegment line (all segments off) the data burst is shown in greaterdetail. In FIG. 10a, the data burst A occurs in timed-relation to theleading edge of the signal on drive line one, immediately after theleading edge. In FIG. 10b, the data burst C occurs in timed-relation tothe leading edge of the signal on drive line one, approximately 40 μsecor so there after. It will be evident to those skilled in the art how adetailed representation of potentials on scanning segment lines forthree segments on; two segments on, one segment off; or one segment on,two segments off would appear.

In FIGS. 11a and 11b there is depicted yet another embodiment. In thisembodiment, the scanning pulses on the segment line potential (FIG. 11a)have the same polarity as in FIG. 8a, but with four level logic as inFIG. 9. The drive line potential floats during the approximately eightymicrosecond periods that scanning pulses are generated on the segmentlines.

In FIGS. 7b-d, 8a-d and 10a-b, it has been suggested that the burst datamay occur one of four different times with respect to the leading edgeof the positive and negative going pulses on a drive line, the differentpulses being identified as A, B, C and D in the aforementioned drawings.It will be evident to those skilled in the art that four differenttimings of these data pulses were selected inasmuch as four columnconductors 14a are depicted in the calculator system of FIG. 5. It willbe evident that if three, five or more column conductors were utilizedthen the number of different timing possibilities for the scanning pulsewith respect to the leading edge on the drive line would be modifiedaccordingly and such modification will be evident to those skilled inthe art. Further, with respect to keyboard 14 in FIG. 5, it has beensuggested that scanning segment lines are attached to the columnconductors 14a and that the segment lines coupled to the row conductors14b are provided with the circuit means for detecting scanning pulsesupon closure of a switch at keyboard 14. It will be evident, however,that the scanning segment lines could just as well be applied to rowconductors 14b and the circuit means for detecting scanning pulses 10ecoupled to column conductors 14a.

Moreover, it will be evident to those skilled in the art that thesuggested periods and potentials of the scanning pulses, and the segmentline signals are a matter of design choice and that a wide range ofperiods and potentials will be found to be operable within the scope ofthis invention.

Still further, it will be evident to those skilled in the art that thesuggested layout of the conductor patterns may be varied as a matter ofdesign choice. For instance, in FIGS. 3a and 4, the pattern of thesegment line conductors for the most significant character position maybe exchanged with the pattern of segment line conductors used in theleast significant character position. Other such modifications will beevident to those skilled in the art.

The invention is not to be limited to the embodiments disclosed, exceptas set forth in the appended claims.

What is claimed is:
 1. A liquid crystal display device comprising:firstand second substrates; liquid crystal material sealed between thesubtrates; a plurality of segment electrodes disposed on a major surfaceof the first substrate; a plurality of segment electrodes disposed on amajor surface of the second substrate in registration with the segmentelectrodes on the first substrate; the segment electrodes being arrangedto provide a row of eight selectively displayable characters includingan end character and seven other characters, each character beingdefined by a pattern of at least seven segment electrodes on eachsubstrate disposed in separately actuable electrode pairs, eachseven-segment character pattern being arranged in a figure-eightconfiguration; the segment electrodes on the first substrate whichdefine the seven other characters being devided into first, second, andthird groups, each group including from one to three segment electrodesper character, each group being restricted to segment electrodes in thesame relative positions of each figure-eight configuration; a firstdrive conductor interconnecting the segment electrodes of the firstgroup; a second drive conductor interconnecting the segment electrodesof the second group; a third drive conductor interconnecting the segmentelectrodes of the third group; the segment electrodes on the secondsubstrate which define the seven other characters being divided intofirst, second and third sets, each set including from one to threesegment electrodes per character, each set being restricted to segmentelectrodes in the same relative positions of each figure-eightconfiguration; a plurality of segment conductors including first,second, and third segment conductors per character respectivelyconnected at each character to the segment electrodes of the first,second and third sets, thereby providing twenty-one segment conductorsconnected to twenty-one separate subsets of segment electrodes on thesecond substrate; each of the segment electrodes on the first substratewhich define the end character being connected to one of the driveconductors; the plurality of segment conductors further including atleast three additional segment conductors each of which is connected toat least one of the segment electrodes on the second substrate whichdefine the end character, one or more of the three additional segmentconductors being connected in common with one or more of the twenty-onesegment conductors of the seven other characters; such that the totalnumber of electrically separate segment conductors plus the number ofdrive conductors is less than or equal to twenty-six, and the segmentconductors and drive conductors are connected to the segment electrodesof the eight characters in such manner that each segment electrode pairis actuable by a unique combination of one of the drive conductors andone of the segment conductors.
 2. The device of claim 1 furthercomprising an integrated circuit chip for driving the segment conductorsand drive conductors, the integrated circuit chip being disposed in atwenty-eight pin package, power connections being made to two pins ofthe package leaving a maximum of twenty-six pins for driving the segmentand drive conductors.
 3. The device of claims 1 or 2:wherein the firstdrive conductor is connected to a first one of the segments electrodesdefining the end character, the second drive conductor is connected to asecond one of the segment electrodes defining the end character, thethird drive conductor is connected to the remaining segments electrodesdefining end character on the first substrate; and wherein theadditional segment conductors comprise five segment conductors, one ofthe five segment conductors being connected to three segment electrodesof the end character and no segment electrodes of the other characters,and the four other segment conductors each being connected to onesegment electrode of the end character and a segment conductor of one ofthe seven other characters.
 4. The device of claim 1 or 2:wherein one ofthe three drive conductors is connected to all of the segment electrodesof the end character; and wherein the additional segment conductorscomprise seven segment conductors, each of which is connected to onesegment electrode of the end character and a segment conductor of one ofthe seven other characters.